The use of rare-earth permanent magnets to provide the excitation field in alternating current (AC) machines is known. However, the handling and mounting of members of rare-earth material is not straightforward. Such members are brittle and are therefore easily damaged. Consequently, it is difficult to mount the members onto a rotor or a stator of an AC machine in such a way that they can withstand the large forces exerted on them during operation, without sustaining damage.
U.S. Pat. No. 6,037,696 discloses a rotor for use in an electrical machine wherein magnetized members are mounted on a surface of a disc-shaped central sheet. The rotor disc of U.S. Pat. No. 6,037,696 includes a braced hub in the form of a spider that is for restraining the central sheet and promoting rotor rigidity. The magnetized members are constrained axially and tangentially on the central sheet by being bonded face-to-face with the surface thereof. The magnetized members are constrained radially on the central sheet by the provision of a circumferential lip that is formed integrally with the central sheet. Further radial constraint is provided by bonding a radially innermost edge of each magnetized member to the braced hub.
It is an object of this invention to address this problem.